toddler getting used to sleeping only in pitch dark

I want to get a slumber pod but I am afraid that once he outgrows it, he will not be able to sleep if it's not pitch dark. Or if it's too hot for him to be completely enclosed in such a tiny space.

We recently travelled where we slept in the basement and it's pitch dark, after we came back he regressed in his sleep in that he is crying and standing up for a long time before he is able to go down by himself. Prior to this travel he was a great sleeper. He is currently 16 months old.

Anyone else has this issue?